Batch loading system for CVD

ABSTRACT

There is provided a method of coating cutting tool inserts by CVD methods with a completely covering coating. During the coating step, the inserts are resting in contact with the support in only a few tiny spots and sufficient space is allowed around each insert to ascertain optimum coating conditions. In a preferred embodiment, each insert rests on a peg allowing a rational production in larger scale and fully automatic CVD loading.

This application is a continuation of application Ser. No. 08/405,782,filed Mar. 17, 1995, now U.S. Pat. No. 5,576,058.

BACKGROUND OF THE INVENTION

The present invention relates to a CVD batch loading method used inconnection with coating of cutting inserts suitable for a rationalproduction in larger scale allowing fully automatic CVD loading.

Chemical Vapor Deposition (CVD) of wear resistant coatings on cementedcarbide inserts has been an industrial practice for more than 20 years.The CVD technique has extensively been discussed in the literature.

In order to minimize the production costs for coated inserts, largesized (10,000-15,000 inserts) CVD batches are generally used. Rationalloading and unloading of the inserts from the CVD reactor is thusrequired. Transportation of the whole load or parts of the load must bepossible to be carried out safely, particularly prior to the coatingoperation.

Another problem related to mass volume CVD is to find an appropriateloading arrangement of the inserts that will allow a well-controlled gasflow through the CVD reactor in order to ensure high and even coatingquality throughout the whole load.

Yet another problem is to avoid contact marks on the inserts formedduring the coating process in the zone between the inserts and theirsupport. Contact marks on the inserts are not acceptable from a cosmeticpoint of view and also since they may deteriorate the cuttingperformance of the coated inserts.

There are many different batch loading systems or methods known in theart.

In one loading arrangement, the inserts are allowed to hang in slits ina tray. This method has the disadvantage of leaving contact marks on theclearance faces of the inserts. The system is unstable and there isalways a potential risk during transportation that the inserts fall overand completely rearrange the packing. In addition, all surfaces of aninsert with this type of loading will not be exposed to the same amountof gas flow during the coating process. This may result in seriousvariation in the coating thickness of any particular insert and hencethe quality of the coating.

In another similar system, the inserts hang between rods. This systemsuffers from the same drawbacks as those mentioned above.

In the so-called net loading arrangement, the inserts are placed onwoven metal nets. The load is built up by piling each metal net on topof each other. When using this method: a) the gas supply to the regionsbetween the inserts and the metal net wire may be insufficient; b) carehas to be taken during transportation to avoid that inserts slidetogether resulting in contact marks between individual inserts; and c)contact marks between the nets and the inserts are always formed.

In yet another method, the inserts are threaded up on a rod. Spacersbetween each insert are generally used to avoid contact between theinserts. The rods may be oriented horizontally or vertically in the CVDreactor. The main drawbacks of this method are the very complicated andtime consuming loading and unloading procedures. Contact marks betweenthe spacer and the insert are difficult to avoid. This method can beapplied to inserts having a central hole for clamping.

In EP 454,686, a loading system is disclosed in which the inserts arestacked on top of each other on a central pin, possibly with a spacerbetween. As a result, the inserts will be only partially coated. Thismethod is aimed for plasma CVD and will not be fully applicable toordinary CVD since the inserts will be "glued" or grown together duringan ordinary CVD process.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of this invention to avoid or alleviate the problems ofthe prior art.

It is further an object of this invention to provide a CVD batch loadingmethod used in connection with coating of cutting inserts suitable for arational production in larger scale allowing fully automatic CVDloading.

In an aspect of the invention there is provided a method of coatingcutting tool inserts by CVD during which coating, the inserts areresting on a support wherein said support is a peg attached to acarrier, said peg comprising a foot portion and a shoulder portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a peg P used in the presently claimedinvention in side view. The peg P consists of a foot A and shoulders Band a neck C and a head D. The shoulders B have a circular as well asnon-circular cross-section such as square, triangular or rectangular butcan also be in the form of wings. The foot A is preferably circular.

FIGS. 2-7 show various embodiments of the presently claimed invention inwhich P=peg, X=carrier, I₁ =insert 1, I₂ =insert 2, I₃ =insert 3, I₄=insert 4, H=hole and F=depression.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The batch loading system according to the presently claimed inventionutilizes a peg attached to a carrier. As a result of this method ofstacking cutting tool inserts in a CVD reactor, complete and evencoating coverage with minimal contact marks on the insert are obtained.

According to the presently claimed invention, an insert I₁ with acentral hole H for clamping, which generally is the case for insertsused for turning, is positioned on a peg P as shown in FIG. 2. Theinsert rests on the peg shoulder B having such a shape that there isminimal contact between the peg and the insert and preferably so thatcontact occurs at only a few tiny points. This can be done by alteringthe shape of the shoulder (e.g., circular, rectangular, square or in theform of wings) depending upon the shape of the hole H or the insertitself. Inside the hole H there is a wide passage around the neck toensure even coating thickness of the inner walls of the hole H. (Thedimension of the hole H is important for a safe fixing of the insertinto its tool holder). The function of the head D which protrudes abovethe top surface of the insert I₁ is to serve as a support for the nextcarrier placed on top (not shown). In case the hole H is straight, thethicker head acts to prevent the insert from tilting from its horizontalposition and touch the upper and/or the lower carrier surfaces. In sometypes of inserts, the hole H is wider at the top surface of the insertand, in that case, a peg without a head can be used. The peg P isattached to the carrier X.

For inserts without a central hole, a loading arrangement according tothe presently claimed invention is illustrated in FIG. 3 for squareinserts I₁, I₂, I₃ and I₄ in which the pegs P are placed between theinserts and generally support at least two inserts. The peg shoulder Bshall have such a shape, e.g., a sharp edge or tip, that the contactarea is minimized.

In one embodiment, a peg P similar to FIG. 1 is used as shown in FIG. 4in which the peg supports an insert only at the middle of the edge. Thisarrangement is preferably used for single sided inserts.

In an alternative embodiment which can be used for positive inserts, apeg shown in FIG. 4 is used. In this case, the peg supports an insertessentially in the middle of each clearance face (FIG. 5).

In yet another alternative embodiment for inserts with a chipbreaker, apeg P as shown in FIG. 6 is used. In this case, the peg P supports theinserts I₁ and I₂ essentially in the bottom of the chipbreaker of eachinsert. The chipbreaker has to be deep enough so as to ensure maximumstability of the loading arrangement. Alternatively, planar inserts canbe provided with a depression between the corners to receive theshoulder of the pegs.

In the various embodiments above, the pegs serve also as support of afollowing carrier. In case such support is provided in other ways, theneck (C) and head (D) can be excluded. In such case, an alternativeembodiment according to FIG. 7 can be used. In this embodiment, insertI₁ is provided with a central hole H (not shown) or depression F of asuitable depth and shape adapted to the peg P.

These embodiments are given as example only. Other embodiments are, ofcourse, possible within the gist of the invention.

Pegs according to the presently claimed invention can be made of arefractory material such as ceramics, reinforced graphite, molybdenumbut are preferably formed of a conventional cemented carbide.

The carrier X may be a woven metal net of, e.g., iron alloy with asuitable mesh size or a tray of graphite or other refractory materialwith mounting holes drilled for the pegs.

The peg foot is snapped into the metal net or pressed into the mountingholes in the tray. A desired number of pegs are mounted in each carrierin a regular pattern. The distance between the pegs as well as theheight of the pegs is selected to give a desired free gas volume aroundeach insert. A free volume around each insert of 1-5 mm is generallysuitable. The carriers are piled on top of each other (preferablyresting on the peg heads) to complete a full CVD load.

When using a tray carrier and a vertical gas flow, holes are suitablydrilled in the trays in the areas between the pegs. The size andpositioning of these holes can be optimized in accordance with knowntechniques so that the gas flow can be controlled and directed in almostany desired way throughout the pile of trays.

When using horizontal or radial gas flows, e.g., when employing theMTCVD (Moderate Temperature CVD) technique, the holes in the trays canoptionally be omitted.

The loading system of the presently claimed invention allows the processgases to reach all essential surfaces of the inserts improving thecoating thickness distribution, minimizing discoloration due toirregular gas flow pattern and reducing coating time. The rigid andexact positioning of the inserts allows a safe transportation prior toand after the coating step and also allows an automatic loading system.By using a suitable cross-section of the shoulders, the only contactbetween the peg and the insert will occur at only a few, less than five,tiny points which are not critical for the performance of the coatedinserts.

In the foregoing description only very few specific details have beengiven by way of examples only. The reason hereto is that the exactconditions depend to a certain extent on the design of the equipment andthe deposition conditions used. It is within the purview of the skilledartisan to adapt the method of the present invention with regard to thedesign and deposition conditions of his equipment.

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed, sincethese are to be regarded as illustrative rather than restrictive.Variations and changes may be made by those skilled in the art withoutdeparting from the spirit of the invention.

What is claimed is:
 1. A method of coating cutting tool insertscomprising:supporting the inserts on a support wherein said supportincludes a peg received in mounting holes of a carrier, said pegcomprising a foot portion and a shoulder portion wherein the peg isplaced between two inserts; and coating the inserts by CVD.
 2. Themethod of claim 1 wherein the inserts include a chipbreaker and thechipbreaker rests on the shoulder portion of the peg.
 3. The method ofclaim 1 wherein the inserts rest on shoulders of a plurality of pegsessentially in the middle of a clearance face of the inserts.
 4. Themethod of claim 1 wherein the inserts rest on shoulders of a pluralityof pegs in the middle of an edge of the inserts.
 5. A method of coatingcutting tool inserts comprising:supporting the inserts on a support,wherein the inserts include a top surface, a bottom surface, and atleast one depression on the bottom surface, wherein said supportincludes a plurality of pegs attached to a carrier, and said pegs arereceived in said depressions to support the inserts during coating; andcoating the inserts by CVD.
 6. The method of claim 5, wherein said atleast one depression is arranged between adjacent corners.
 7. The methodof claim 5, wherein said at least one depression is arranged centrally.